The splendid granite chimney stack on Ballycorus hill is a landmark familiar to generations of south Dubliners - but it is likely that many people today have no idea why or when it was built.
For the Ballycorus chimney is a remnant of a forgotten industrial age in this area. Built in 1858, its function was to safely disperse the noxious vapours generated at a lead works in the valley below.
Ballycorus lies amid rolling greenery between Kilternan and Shankill. Lead mining began here, on the west side of the hill, around 1806. Initially there was a small open-cast or surface working of two veins of galena-rich ore discovered at the edge of the Leinster granite. But by 1820 excavations had extended deep into the hillside, and the ore raised was being smelted locally to extract the metallic lead.
In 1825 the newly-formed Mining Company of Ireland (MCI) took over operations at Ballycorus. It sank several new exploratory shafts and invested heavily in expanding the smelter works to cater for the output from its other mines in Wicklow, Wexford and Donegal. The works complex soon boasted two furnace houses operating round the clock, rolling and pipe mills, a shot tower, extensive storage bunkers and a silver refinery. Also integrated into the site were 11 workers' cottages and a manager's house. By 1859 there were 130 people employed at Ballycorus, and the MCI decided to sponsor a new local national school to serve the works community.
The Ballycorus operations are described in Sir Robert Kane's 1844 book The Industrial Resources of Ireland. The ore from the mine was then being manufactured into the lead pipes and sheeting used in the Dublin construction industry. Power for the machinery came from the Loughlinstown River via a millpond and watercourse. Nearby, a separate shot factory produced the small spheres of lead used in shotguns.
The local mine, however, eventually proved to be unprofitable, and despite renewed explorations discovering a deep rib of native silver there in 1843, it had been abandoned by 1860.
However, smelting continued until 1913, mostly processing ore from the Luganure mines near Glendalough, which after 1862 was carried by train to Shankill. When that source ran out ore was imported from the Isle of Man via Bray.
Expansion during the 1860s included a new shot manufactory complete with a fine shot tower. Shot was made by dropping molten lead through a riddle at the top into a tank of water far below. It cooled into spherical pellets which were then separated and graded. It is a pity that this tower, a rather elegant 37 metre-high structure that had the appearance of a lighthouse on the hillside, was demolished around 1930. The smelting works closed when the company relocated to be closer to Dublin port.
The surviving landmark chimney - about 26 metres tall and 235 metres above sea level - replaced a now vanished 1836 vent system on the lower slopes which had caused pollution in the area. Old photographs show it was about a third taller before its top section, along with parts of the external spiral cantilever staircase and viewing veranda, was removed for safety reasons.
A unique feature at Ballycorus is the above-ground granite arched flue which connected the works' underground flues to the chimney - a run of some 1.4 km. Originally there were metal doors at 50-metre intervals to allow recovery of the valuable "dust" which condensed on the interior brickwork. The recycled sweepings were worth £1,400 a year - a return which allowed the MCI to recover the cost of its construction very quickly. The effects on workers' health will never be known.
These days it is just the chimney which attracts hill-walkers, but much related industrial archaeology can still be traced. A track down through the gorse brings you to the top of Mine Hill Lane, along which an overgrown but mostly intact stretch of flue runs all the way to the works site. Here the many individual buildings are now converted, derelict, or gone altogether, but the extent of the original complex is discernable, and two distinctive granite pillars still guard its main entrance. The attractive cut-granite manager's house survives, as do the cottages, gate lodge, old schoolhouse, watercourse and millpond.
Back on the hillside the 1860s shot manufactory is now a private residence, while on the upper slopes the scar and spoils of the early open-cast mine remain - to this day devoid of natural vegetation.
An interesting summer ramble, Ballycorus hill and chimney are reached after an easy climb from the Coillte car park at Carrickgollogan, and an added bonus is the majestic panorama from the nearby summit of the same name.